Technical Field
The present invention relates to an LED driving device and an LED lighting apparatus using the same.
Background Art
Light-emitting diode (LED) elements are beginning to be used as a light source for backlight for a liquid crystal display device or a luminaire such as a street light. In particular, an LED lighting apparatus of a fluorescent-tube or bulb type using white LED elements is under development as a luminaire replacing an incandescent bulb or a fluorescent tube. An LED driving device constituting such an LED lighting apparatus is required to supply a predetermined amount of power to the LED elements with high precision.
The LED driving device also performs color control operation for obtaining various colors by using several emission colors. In this case, the color control operation is often controlled by a microcomputer or the like.
FIG. 1 is a circuit diagram showing a circuit configuration of an example of a conventional LED driving device described in Japanese Patent Application Publication No. 2010-282757. A conventional LED lighting device 100 shown in FIG. 1 includes a commercial power source 102, a power-source switch 103, a microcomputer power source 104, a rectifying circuit 111, a DC power source circuit 112, a power-source synchronizing circuit 113, a microcomputer 114, a non-volatile memory 115, a white LED lighting circuit 121, a red LED lighting circuit 122, and MOSFETs (switching elements) 131.
The white LED lighting circuit 121 having series-connected white LEDs and the red LEDs lighting circuit 122 having series-connected red LEDs are connected to an output side of the DC power source circuit 112. Each of the white LED lighting circuit 121 and the red LED lighting circuit 122 has the MOSFET 131 connected to its LEDs in series.
The rectifying circuit 111 is a diode bridge circuit and is configured to rectify an AC voltage of the commercial power source 102 into a DC voltage and output the DC voltage to the DC power source circuit 112. Based on control by the microcomputer 114, the DC power source circuit 112 converts the DC voltage from the rectifying circuit 111 into a predetermined DC voltage and supplies it to the white LED lighting circuit 121 and the red LED lighting circuit 122.
The microcomputer 114 controls on and off of the MOSFETs 131 to control the brightness of the white LEDs and the red LEDs. The microcomputer 114 is configured to detect a temporary-stop control in which the power-source switch 103 is switched off and then switched on again within a predetermined period of time. Upon detection of the temporary-stop control, the microcomputer 114 performs brightness control by lighting at least one group of the white LEDs and the red LEDs at an illuminance different from that used before the power-source switch 103 is switched off.
FIG. 2 is a diagram showing a circuit configuration of another example of a conventional LED driving device described in Japanese Patent Application Publication No. 2012-155900. A conventional luminaire 10 shown in FIG. 2 includes multiple light sources 45 to 48 (LEDs of first to fourth colors) each configured to emit light of a color different from those emitted by the other light sources and a light-source lighting circuit 37 configured to control the brightness of the light from the multiple light sources 45 to 48 by mixing their colors until turning them off. By its brightness control operation, after one of the light sources 45 and 46, e.g., the light source 45, reaches a lower limit of brightness control, the light-source lighting circuit 37 turns off both of the light sources 45 and 46 when the other one, namely the light source 46, reaches a lower limit of brightness control.
In addition, a microcomputer peripheral circuit unit 50 controls first to fourth circuit blocks 41 to 44 to light the multiple light sources 45 to 48.
However, the LED driving devices described in Japanese Patent Application Publication Nos. 2010-282757 and 2012-155900 have complicated circuit configurations since the color control operation is controlled by the microcomputer.
Moreover, even in a case where only two colors, such as a daylight color and a warm color, are subjected to the color control, the circuit configuration is still complicated due to the use of the microcomputer.
An objective of the present invention is to provide an LED driving device and an LED lighting apparatus which are inexpensive and capable of color control operation with a simple circuit having no microcomputer.